1. Overview

1.概述

Data compression is a crucial aspect of software development that enables efficient storage and transmission of information. In Java, the Deflater and Inflater classes from the java.util.zip package provide a straightforward way to compress and decompress byte arrays.

数据压缩是软件开发的一个重要方面，它可以实现信息的高效存储和传输。在 Java 中，来自 java.util.zip 包的 Deflater 和 Inflater 类提供了压缩和解压缩字节数组的直接方法。

In this short tutorial, we’ll explore how to use these classes with a simple example.

在这个简短的教程中，我们将通过一个简单的示例来探讨如何使用这些类。

2. Compressing

2.压缩

The Deflater class uses the ZLIB compression library to compress data. Let’s see it in action:

Deflater 类使用 ZLIB 压缩库来压缩数据。让我们来看看它的实际应用：

public static byte[] compress(byte[] input) {
    Deflater deflater = new Deflater();
    deflater.setInput(input);
    deflater.finish();

    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    byte[] buffer = new byte[1024];

    while (!deflater.finished()) {
        int compressedSize = deflater.deflate(buffer);
        outputStream.write(buffer, 0, compressedSize);
    }

    return outputStream.toByteArray();
}

In the above code, we’ve used several methods of the Deflater class to compress the input data:

在上述代码中，我们使用了 Deflater 类的多个方法来压缩输入数据：

setInput(): set input data for compression
finish(): indicate that compression should end with the current contents of the input
deflate(): compress the data and fill to a specified buffer, then return the actual number of bytes of compressed data
finished(): check if the end of the compressed data output stream has been reached

Additionally, we can use the setLevel() method to get better compression results. We can pass values from 0 to 9, corresponding to the range from no compression to best compression:

此外，我们还可以使用 setLevel() 方法获得更好的压缩效果。我们可以传递从 0 到 9 的值，对应于从无压缩到最佳压缩的范围：

Deflater deflater = new Deflater();
deflater.setInput(input);
deflater.setLevel(5);

3. Uncompressing

3.解压缩

Next, let’s decompress a byte array with the Inflater class:

接下来，让我们使用 Inflater 类解压字节数组：

public static byte[] decompress(byte[] input) throws DataFormatException {
    Inflater inflater = new Inflater();
    inflater.setInput(input);

    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    byte[] buffer = new byte[1024];

    while (!inflater.finished()) {
        int decompressedSize = inflater.inflate(buffer);
        outputStream.write(buffer, 0, decompressedSize);
    }

    return outputStream.toByteArray();
}

This time, we used three methods of the Inflater class:

这次，我们使用了 Inflater 类的三个方法：

setInput(): set input data for decompression
finished(): check if the end of the compressed data stream has been reached
inflate(): decompress bytes into the specified buffer and return the actual number of bytes uncompressed

4. Example

4.示例

Let’s try out our methods with this simple example:

让我们用这个简单的例子来试试我们的方法：

String inputString = "Baeldung helps developers explore the Java ecosystem and simply be better engineers. "
  + "We publish to-the-point guides and courses, with a strong focus on building web applications, Spring, "
  + "Spring Security, and RESTful APIs";
byte[] input = inputString.getBytes();

byte[] compressedData = compress(input);

byte[] decompressedData = decompress(compressedData);

System.out.println("Original: " + input.length + " bytes");
System.out.println("Compressed: " + compressedData.length + " bytes");
System.out.println("Decompressed: " + decompressedData.length + " bytes");

assertEquals(input.length, decompressedData.length);

The result will look like this:

结果将是这样的

Original: 220 bytes
Compressed: 168 bytes
Decompressed: 220 bytes

5. Conclusion

5.结论

In this article, we’ve learned how to compress and uncompress a Java byte array using the Deflater and Inflater classes, respectively.

在本文中，我们学习了如何分别使用 Deflater 和 Inflater 类压缩和解压缩 Java 字节数组。

The example code from this article can be found over on GitHub.

本文的示例代码可以在 GitHub 上找到。